1. Technical Field
This disclosure relates to an image forming apparatus, and more specifically to an image forming apparatus capable of performing borderless image formation and duplex image formation and operation control of the image forming apparatus.
2. Description of the Related Art
Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional devices having, e.g., two or more of the foregoing capabilities. In such an image forming apparatus, a toner adheres to a front face of a transfer member for transferring an image onto a transfer sheet or the like, particularly to a secondary transfer member of an intermediate transfer type due to contact with a toner pattern or toner dirt on an intermediate transfer member in some cases. For this reason, for example, JP-2001-312154-A proposes a technique for providing a cleaning mechanism for removing the adhering toner. In particular, in a case in which an image of a toner pattern is formed in an inter-sheet area to control toner density, the toner adhesion to the front face of the intermediate transfer member is remarkable. Therefore, the cleaning mechanism is indispensable.
Typically, brush cleaning or blade cleaning is used as the cleaning mechanism. In some cases, however, a roller member having a relatively small diameter is used for the secondary transfer member in order to enhance separation performance of a sheet. Such a configuration may hamper cleaning of a front face of a thin roller-shaped member. As a result, the toner adhering to the secondary transfer member may stick to a back face of a conveyed sheet, thus making the back face of the sheet dirty. One approach to enhance cleaning performance includes a technique for coating the front face of the secondary transfer member with a material having an excellent mold release characteristic or applying a lubricant onto the front face. However, such approach causes an increase in cost and size of the apparatus.
For example, JP-H08-248787-A discloses, as an approach to prevent the foregoing, the technique for applying a bias having a reverse polarity to a transfer bias to prevent a toner from adhering to a transfer member in order to inhibit a back face of a sheet from becoming dirty. Moreover, JP-2006-308816-A discloses the technique for returning a toner once adhered to a secondary transfer member to an intermediate transfer body through a bias, thereby carrying out cleaning, for example. However, these techniques are insufficient for preventing the toner adhesion from being caused by the toner pattern of which image is formed in the inter-sheet area. Therefore, JP-2012-018369-A discloses the technique for separating a secondary transfer member from an intermediate transfer body in an inter-sheet area when forming an image of a toner pattern in the inter-sheet area, as an approach for forming the image of the toner pattern in the inter-sheet area, being utilized for density detection control in continuous image formation or prevention of deterioration in the image through replacement of a toner, and inhibiting the secondary transfer member from being contaminated with the toner without providing an expensive cleaning mechanism in the secondary transfer member, for example.
On the other hand, in recent years, a demand for borderless image formation has been increased. Referring to the borderless image formation according to the related art, there has been carried out a work for forming an image on a sheet of a size larger than a standard size and then removing a margin part. In order to simplify the work, however, the necessity for the borderless image formation has been increased. The technique for carrying out the borderless image formation includes a technique for forming an image to reach edges of a sheet and conveying the sheet with high positional precision, the technique disclosed in JP-2006-220991-A for detecting a sheet conveyance position to adjust an image formation area, for example, and the technique disclosed in JP-2004-045457-A for forming an image framing out from a sheet on the assumption that a conveyance position varies to some extent, for example.
Such an image forming apparatus described in JP-2004-045457-A or the like is capable of performing a bordered print mode for forming an image on a sheet so as to have a margin on a border around a whole periphery of a sheet and a borderless print mode for forming an image so as to have no margin on the border around the whole periphery of the sheet or any border.
In the techniques, however, a unit for controlling sheet conveyance with high precision increases a cost and a size of an apparatus, and it may be difficult to detect a sheet conveyance position with high precision in a high-speed machine of a high conveyance speed. In the case in which the image is formed framing out from the sheet, moreover, the front face of the secondary transfer member may be contaminated with the stray toner, causing contamination of the back face or a cut end. In order to prevent such a problem, for example, cleaning is performed on the front face of the secondary transfer member. However, as describe above, it is technically difficult to clean the secondary transfer member by the cleaning member. enhancing the performance may cause an increase in the cost and the size of the apparatus.
Furthermore, if the borderless image formation is performed in a state in which a leading end part of a sheet has no border, the sheet may be wound around a fixing member in an electrophotographic apparatus. For this reason, a margin is generally provided in the leading end part of the sheet. If duplex image formation is carried out when an image is formed with a trailing end of the sheet having no border, however, the trailing end on a front face side acts as a leading end on a back face side and enters the fixing member in a state in which the leading end of the sheet has a toner. Also in this case, consequently, the sheet may be wound around the fixing member, thus hampering execution of the borderless image formation and the duplex image formation at the same time.
For the image forming apparatus capable of executing the bordered print mode and the borderless print mode like that described in JP-2004-045457-A, generally, the bordered print mode is selected as initial setting. In the case in which the borderless print mode is executed, an operator selects the borderless print mode through a touch panel or the like and carries out switching from the bordered print mode to the borderless print mode. For this reason, even if there are needs for always performing the borderless printing for a sheet of a specific one of various types, the operator selects the borderless print mode at each time, thus increasing the operation burden of the operator.